Autostereoscopic display apparatus

ABSTRACT

An autostereoscopic display apparatus includes a spatial light modulator in which alignment features such as bump features provide radially symmetric alignment of the molecules of the liquid crystal. A parallax element is arranged over the spatial light modulator to direct light from the pixels into different viewing windows. The apertures of the pixels are shaped such that, for each individual row of pixels, a notional line parallel to the geometric axes of the parallax elements has a total length of intersection with the pixels of the row, weighted for the intensity of light modulated by the alignment features, which is the same for all positions of the notional line. This improves angular intensity uniformity. The pixels may each include plural apertures, wherein the alignment features of the apertures of each individual pixel are offset from one another in a direction perpendicular to said geometric axes. This improves angular contrast uniformity.

RELATED APPLICATIONS

This application claims priority to British Application Serial Number1001344.9, filed Jan. 27, 2010, which is herein incorporated byreference.

BACKGROUND

1. Field of Invention

The present invention relates to pixel structures for anautostereoscopic display apparatus. Such a display apparatus may be usedin televisions, computer monitors, telecommunications handsets, digitalcameras, laptop and desktop computers, games apparatus, automotive andother mobile display applications.

2. Description of Related Art

Normal human vision is stereoscopic, that is each eye sees a slightlydifferent image of the world. The brain fuses the two images (referredto as the stereo pair) to give the sensation of depth. Three dimensional(3D) stereoscopic displays show a separate image to each of the eyescorresponding to that which would be seen if viewing a real world scene.The brain again fuses the stereo pair to give the appearance of depth inthe image.

FIG. 1 shows in plan view a display surface in a display plane 1. Aright eye 2 views a right eye homologous image point 3 on the displayplane and a left eye 4 views a left eye homologous point 5 on thedisplay plane to produce an apparent image point 6 perceived by the userbehind the screen plane. If light from point 3 is seen by the left eye 4and light from the point 5 is seen by the right eye 2 then apseudoscopic image point 21 is produced. Pseudoscopic images areundesirable as they produce visual strain to observers.

FIG. 2 shows in plan view a display surface in a display plane 1. Aright eye 2 views a right eye homologous image point 7 on the displayplane and a left eye 4 views a left eye homologous point 8 on thedisplay plane to produce an apparent image point 9 in front of thescreen plane. Pseudoscopic image point 12 is produced if the right eye 2can see light from point 8 and the left eye 4 can see light from point7.

FIG. 3 shows the appearance of the left eye image 10 and right eye image11. The homologous point 5 in the left eye image 10 is positioned on areference line 12. The corresponding homologous point 3 in the right eyeimage 11 is at a different relative position 3 with respect to thereference line 12. The separation 13 of the point 3 from the referenceline 12 is called the disparity and in this case is a positive disparityfor points which will lie behind the screen plane. Similarly in the lefteye image 10, the homologous point 8 is positioned on a reference line14 while in the right eye image the corresponding homologous point 7 islaterally separated from the reference line 14 by a distance 15 with anegative disparity. Changing from the left eye image 10 to the right eyeimage 11, the movement of the homologous point 3 is to the right. Thiscorresponds to an orthoscopic image point 6 behind the screen plane,while the movement of the homologous point 7 is to the left,corresponding to an orthoscopic image point 9 in front of the screenplane.

For a generalised point in the scene there is a corresponding point ineach image of the stereo pair as shown in FIG. 3. These points aretermed the homologous points. The relative separation of the homologouspoints between the two images is termed the disparity; points with zerodisparity correspond to points at the depth plane of the display. FIG. 1shows that points with uncrossed disparity appear behind the display andFIG. 2 shows that points with crossed disparity appear in front of thedisplay. The magnitude of the separation of the homologous points, thedistance to the observer, and the observer's interocular separationgives the amount of depth perceived on the display.

Stereoscopic type displays are well known in the prior art and refer todisplays in which some kind of viewing aid is worn by the user tosubstantially separate the views sent to the left and right eyes. Forexample, the viewing aid may be color filters in which the images arecolor coded (e.g. red and green); polarising glasses in which the imagesare encoded in orthogonal polarization states; or shutter glasses inwhich the views are encoded as a temporal sequence of images insynchronisation with the opening of the shutters of the glasses.

Autostereoscopic displays operate without viewing aids worn by theobserver. In autostereoscopic displays, each of the views can be seenfrom a limited region in space as illustrated in FIG. 4.

FIG. 4 shows a display device 16 with an attached parallax element 17.The display device 16 produces a right eye image 18 for the right eyechannel. The parallax element 17 directs light in a direction shown bythe arrow 19 to produce a right eye viewing window 20 in the region infront of the display. An observer places their right eye 22 at theposition of the window 20. The position of the left eye viewing window24 is shown for reference. The viewing window 20 may also be referred toas a vertically extended optical pupil.

FIG. 5 shows the left eye optical system. The display device 16 producesa left eye image 26 for the left eye channel. The parallax element 17directs light in a direction shown by the arrow 28 to produce a left eyeviewing window 30 in the region in front of the display. An observerplaces their left eye 32 at the position of the window 30. The positionof the right eye viewing window 20 is shown for reference.

The parallax element 17 acts as an optical steering mechanism. The lightfrom the left image 26 is sent to a limited region in front of thedisplay, referred to as the viewing window 30. If a left eye 32 isplaced at the position of the viewing window 30 then the observer seesthe appropriate left eye image 26 produced by the display device 16.Similarly the optical system sends the light intended for the rightimage 18 to a right eye viewing window 20. If the observer places theirright eye 22 in that window then the right eye image 18 produced by thedisplay device 16 will be seen. Generally, the light from either imagemay be considered to have been optically steered (i.e. directed) into arespective directional distribution.

In this application the term “3D” is used to refer to a stereoscopic orautostereoscopic image in which different images are presented to eacheye resulting in the sensation of depth being created in the brain. Thisshould be understood to be distinct from “3D graphics” in which a 3Dobject is rendered on a two dimensional (2D) display device and each eyesees the exact same image.

The parallax element 17 may be switchable between a state in which itprovides a 3D image and a state in which it has substantially no opticaleffect to allow selective display of 3D and 2D images. In thisapplication the term “2D/3D” is used to refer to a display apparatus inwhich the function of the optical element can be so switched to enable afull resolution 2D image or a reduced resolution autostereoscopic 3Dimage.

FIG. 6 shows in plan view a display apparatus comprising a displaydevice 16 and parallax element 17 in a display plane 34 producing theleft eye viewing windows 36, 37, 38 and right eye viewing windows 39,40, 41 in the viewing window plane 42. The separation of the windowplane from the display device 16 is termed the nominal viewing distance43. The viewing window 37 and viewing window 40 in the central positionwith respect to the display device 16 are in the zeroth lobe 44. Lefteye viewing window 36 and right eye viewing window 39 located to theright of the zeroth lobe 44 are in the +1 lobe 46, while left eyeviewing window 38 and right eye viewing window 41 located to the left ofthe zeroth lobe are in the −1 lobe 48.

The viewing window plane 42 of the display apparatus represents thedistance from the display device 16 at which the lateral viewing freedomis greatest. For points away from the display plane 34, there arediamond shaped autostereoscopic viewing zones, as illustrated in planview in FIG. 6. As can be seen, the light from each of the points acrossis beamed in a cone of finite width to the viewing windows. The width ofthe cone may be defined as the angular width.

The parallax element 17 serves to generate a directional distribution ofthe illumination at the viewing window plane 42 at a defined distance 43from the display device 16. The variation in intensity across theviewing window plane 42 constitutes one tangible form of a directionaldistribution of the light.

If an eye is placed in each of a pair viewing zones such as left eyeviewing window 37 and right eye viewing window 40, then anautostereoscopic image will be seen across the whole area of thedisplay. To a first order, the longitudinal viewing freedom of thedisplay is determined by the length of these viewing zones.

The variation in intensity (or luminance) α 50 across the window planeof a display (constituting one tangible form of a directionaldistribution of the light) is shown with respect to position x 51 foridealised windows in FIG. 7. The right eye window position intensity (orluminance) function (or distribution) 52 corresponds to the right eyeviewing window 41 in FIG. 6, and intensity (or luminance) function 53corresponds to the left eye viewing window 37, intensity (or luminance)function 54 corresponds to the right eye viewing window 40 and intensity(or luminance) function 55 corresponds to the left eye viewing window36. The integrated intensity (or luminance) function, 60 is the sum ofthe intensity (or luminance) from the individual intensity (orluminance) function 52, 53, 54, 55 with respect to the locations of theindividual windows 41, 37, 40, 36 and further adjacent windows.

FIG. 8 shows the integrated intensity function 60 with position x 51schematically for more realistic windows. The right eye window positionintensity function 56 corresponds to the right eye viewing window 41 inFIG. 6, and intensity function 57 corresponds to the left eye viewingwindow 37, intensity function 58 corresponds to the right eye viewingwindow 40 and intensity function 59 corresponds to the left eye viewingwindow 36. The ratio of the variation from an integrated nominalintensity function 60 to the nominal intensity in an angular range istermed the angular intensity uniformity (AIU) or alpha (α) function. Thenominal intensity function may be for example a flat Luminance functionas shown in FIG. 7, a Lambertian function, or some other function with asubstantially smoothly varying intensity profile. The AIU may bemeasured over a limited range of viewing angles, or over the entireangular range of output angles of the respective display.

FIG. 9 shows a further intensity function 61 in which substantiallytriangular shaped viewing windows are overlapped in order to produce aflat integrated intensity (or luminance) function 60. Advantageously,such windows can provide a robust means by which to reduce nonuniformities in the function 60. Further such windows reduce imageflipping artefacts in which the image content appears to rapidly changefrom one view to another in multi-view displays, causing an apparentrotation of the image to an observer.

Several 3D artefacts can occur due to inadequate window performance,particularly for overlapping windows. Pseudoscopic images occur whenlight from the right eye image is seen by the left eye and vice versa.This is a significant 3D image degradation mechanism that can lead tovisual strain for the user. Overlapping windows are seen as image blur,which limits the useful amount of depth that can be shown by thedisplay. Additionally, poor window quality will lead to a reduction inthe effective viewing freedom of the observer. The optical system isdesigned to optimise the performance of the viewing windows.

In displays with multiple views, adjacent windows contain a series ofview data. As an observer moves laterally with respect to the displaydevice, the images seen by each eye vary so that the appearance of a 3Dimage is maintained. Human observers are sensitive to variation inluminance as they move with respect to the display. For example, if theintegrated intensity (or luminance) function 60 varies by more than0.5%-5% of the maximum, then the display will appear to flicker. Thus itis desirable to minimise the variation of the integrated intensity (orluminance) function 60. As the function varies with the viewing angle,the uniformity of the function may be referred to as the angularintensity uniformity (AIU) which is an important performance parameter.

The respective images are displayed at the display plane 34, andobserved by an observer at or near the viewing window plane 42.

There will now be discussed some known techniques for improving the AIUof a display.

One type of prior art pixel configuration for autostereoscopic displayapparatus uses the well known stripe configuration as shown in FIG. 10 aas used for standard 2D displays. The pixels apertures 62 are arrangedin columns of red pixels 65, green pixels 67 and blue pixels 69. Togenerate an autostereoscopic display, a parallax element 172 such as alenticular array is aligned with groups of color pixels 65, 67 and 69 asshown. The cusp 71 between the lenses of the array is one example of thegeometric axis of the array of parallax elements.

The parallax element 172 may be slanted so that the geometric axes ofthe optical elements (e.g. lenses in the case of a lenticular array) ofthe parallax element 172 are inclined to the vertical column directionof the pixel apertures 62, as described for example in U.S. Pat. No.3,409,351 and U.S. Pat. No. 6,064,424. Such an arrangement enablesoverlapping of windows, similar to that shown in FIG. 9, that results ina better uniformity of the integrated intensity (or luminance) function60 of intensity compared to a parallax element in which the geometricaxes of the optical elements are parallel to the vertical columndirection of the pixel apertures.

Herein, a line parallel to the geometric axes of the optical elements ofa parallax element is termed a “ray line”, being a line along which raysof light are nominally (ignoring aberrations) directed from a displaydevice to the same relative horizontal position in the viewing windowplane at any one vertical position in the viewing window plane, ratherthan being the direction of a ray of light. FIG. 10 a further shows theinclined orientation of the ray lines 64 and the geometric axes of theoptical elements of the parallax element 172 with respect to the pixelapertures 62. Such an arrangement will generate windows that are tiltedwith respect to the vertical such that the view data will appear tochange as the observer moves vertically.

FIG. 10 a further includes a graph of the resultant overlap (orintersection) of ray lines 64 with the pixel aperture function providingan intensity function termed herein the zeta (ζ) function 73. The zeta(ζ) function 73 varies with position y 49 in the pixel plane. As will bedescribed below, this is related to the window intensity function alpha(α) 50 at positions x 51 across the window plane 42.

For ease of understanding, the positions y 49 where a ray line 64crosses the function 75 correspond to horizontal position y 49 intowhich light is directed from the ray line 64. The intensity function 75of the zeta (ζ) function 73 has an intensity which is generally flat butwhich has peaks 74 whose origin has been appreciated as follows.

The zeta (ζ) function at each given position y 49 can be determined bymeasuring the total intersection length 66, 68, 70, 72 (shown in boldlines) of the ray lines 64 corresponding to that position y 49 acrossadjacent pixel apertures 62. This is because, in operation, the parallaxelement 172 collects light from a ray line 64 and directs it all towardsa position in space where that light is observed by the viewer.

In fact an eye receives light from a bundle of ray lines 64 from aregion, or spot at the pixel plane due to the pupil size, lensaberrations and lens focus condition so the actual window integratedintensity function alpha (α) 60 observed is a convolution of the zeta(ζ) function 73 with the spot function, sigma (σ), but this will stillhave similar peaks. Thus as the integrated intensity function 60 variesas the total intersection length varies due to the ray line 64 varyinglycovering different amounts of the pixel apertures 62 and the gapstherebetween. In particular, the intensity function 75 includes elevatedlevels where the total intersection length is high because the ray line64 intersects more of the pixel apertures 62 in the corner thereof.

As can be seen, the total intersection length 66, 68, 70, 72 can includecontributions from two adjacent pixel apertures 62. While these adjacentpixels may have two different colors, each will have a correspondingpixel of the same color in the unit cell structure of the 3D image. So,the adjacent pixels can conveniently be used to form an understanding ofthe total intersection length within a single color.

In some known systems with non-uniform zeta (ζ) intensity function 75where the parallax element 172 is a lenticular array, the lenses may bedefocussed in order to smooth the alpha (α) integrated intensityfunction 60, effectively by providing an average of the differentintersection lengths 66 of different ray lines 64. However, such anapproach creates an increased overlap between the 3D windows and resultsin increased levels of image blur, reduced useful depth and increasedpseudoscopic images. It is therefore desirable to maintain a high AIUwithout increasing the defocus of the lenses.

WO-2007/031921 discloses a technique by which the features such as peaks74 in the intensity function 75 are reduced by means of a pixel cut-out76 as shown in FIG. 10 b. The cut-out 76 compensates for the increasedintersection which otherwise occurs in the corner of the pixel aperture62 reducing the total intersection length 78 for those ray lines 80 andthereby flattening the zeta (ζ) intensity function 75. However, such anarrangement cannot be used to compensate the output of wide viewingangle displays, as will be shown below.

Conventional Liquid Crystal Display (LCD) panels such as twisted nematicLiquid Crystal Display (TN-LCD) with homogeneous alignment usesubstantially rectangular pixel aperture shapes in which the whole ofthe pixel operates as a single domain such that the angular contrastproperties of the optical output are substantially constant for eachpart of the pixel. Such pixels are well suited to the rectangular cutoutapproach to improve uniformity of integrated intensity function 60.However, such panels suffer from significant variations of contrast withviewing angle due to the restrictions of the optical performance of asingle liquid crystal alignment domain within the cell. To compensatefor such viewing angle effects, one approach is to use Vertical Aligned(VA) LC materials in combination with multiple domain structures andfurther complex alignment modification techniques. In this case eachpixel comprises plural domains having different alignments of the liquidcrystal molecules. The contrast properties with viewing angle of thedisplay are determined by the addition of contrast properties from theindividual domains.

One approach for improving the AIU is for the display to implement aradially symmetric mode. In this case, the apertures (displaying area)of the pixels of the spatial light modulator comprise an alignmentfeature, such as a bump feature, that provides radially symmetricalignment of the molecules of the liquid crystal. In general such adisplay has the capability of improving the angular characteristics ofthe display apparatus.

SUMMARY

According to the present invention, there is provided anautostereoscopic display apparatus comprising:

a spatial light modulator having an array of individually addressablepixels of different colors arranged in rows and columns, each pixelcomprising at least one aperture that contains liquid crystal and has analignment feature arranged to provide radially symmetric alignment ofthe molecules of the liquid crystal; and

a parallax element comprising an array of optical elements arranged overthe spatial light modulator to direct light from the pixels intodifferent viewing windows, the optical elements having geometric axesextending in parallel across the spatial light modulator transversely tosaid rows in which the pixels are arranged;

wherein the apertures are shaped such that a notional line parallel tothe geometric axes of the parallax elements has a total length ofintersection with the pixels of the same color that are adjacent alongthe notional line, which total length of intersection is the same forall positions of the notional line, when the length of intersection isweighted across said alignment features by the intensity of lightmodulated by the alignment feature expressed as a fraction of theintensity of light modulated by the remainder of the pixel.

This improves the AIU and ACU of the display apparatus as a result ofthe total intensity weighted length of intersection of notional linesparallel to the geometric axes of the cylindrical lenses with eachindividual pixel, being the same for all positions of the notional line.In operation, the parallax element collects light from one of thenotional lines (a ray line) and directs it all towards a position inspace where that light is observed by the viewer (or more strictlyspeaking an eye receives light from a bundle of ray lines due to thepupil size, lens aberrations and lens focus condition so the actualintensity observed is a convolution with the zeta (ζ) function). Thus,the total intersection length being the same for all positions of thenotional line means that the intensity of the observed light is the samefor different viewing positions when each pixel has the sametransmission setting (for example on a white image). In achieving thiscondition, the length of intersection is weighted across said alignmentfeatures by the intensity of light modulated by the alignment featureexpressed as a fraction of the intensity of light modulated by theremainder of the pixel. This is based on an appreciation of thephenomenon that the bump alignment feature might not provide the sameintensity as the remainder of the pixel and compensates for thatphenomenon.

Advantageously, each pixel comprises plural apertures, each of whichcomprises liquid crystal and a said alignment feature in the liquidcrystal, wherein the alignment features of the apertures of eachindividual pixel are offset from one another in a directionperpendicular to said geometric axes.

With this feature, the ACU for different viewing angles is improved forthe following reason. This advantage arises because the alignmentfeatures provide radially symmetric alignment of the molecules of theliquid crystal. As a result, each of the notional lines crossesmolecules of the liquid crystal that are aligned differently, dependingon the position of the notional line with respect to the alignmentfeature. The different alignment causes variation in the contrast of thelight collected from the different notional lines and observed by aviewer at a corresponding viewing position, hence generating angularcontrast non-uniformities. The uniformity of contrast with respect toposition x 51 in the window plane is termed the angular contrastuniformity, ACU or beta (β) function. However, this effect is reduced bythe alignment features of the apertures of each individual pixel beingoffset from one another in a direction perpendicular to said geometricaxes. In particular, across the range of possible positions of thenotional lines, there is an averaging of the alignment of molecules ofliquid crystal so that variations in contrast with viewing angle areminimized.

In addition, these advantages may be achieved without the need todefocus the optical elements, enabling the focus of the parallax elementto be set to provide a small image of a notional observer's eye at thepixel plane so as to reduce blurring between viewing windows.Advantageously this improves 3D image quality by reducing the intensityof pseudoscopic images and also reduces the blur of images themselves.

The enhanced AIU and ACU improve the performance of the displayapparatus. It may provide various advantages depending on theconfiguration of the display apparatus. Such advantages include, forexample reducing image blur, and/or allowing increased levels of depthto be shown. The invention has particular value in an autostereoscopicmultiview display apparatus in enabling the display apparatus to be freeof visible flicker for a moving observer. Thus an observer moving withrespect to the display will not see the display appear to flicker asthey move, or see intensity changes across the display area.

In a switchable 2D/3D autostereoscopic display apparatus, besides suchadvantages in the 3D mode, the AIU and ACU in the 2D mode may also beimproved; and the manufacturing and design of switchable parallaxelement may be relaxed; having the results of lower cost, higher yieldand/or relaxed tolerances. In a switchable 2D/3D autostereoscopicdisplay apparatus, using a birefringent lens array as the parallaxelement, the refractive index matching requirement of the lens array maybe relaxed and/or the polarization switcher performance at high anglesmay be relaxed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 shows the generation of apparent depth in a 3D display for anobject behind the screen plane;

FIG. 2 shows the generation of apparent depth in a 3D display for anobject in front of the screen plane;

FIG. 3 shows the position of the corresponding homologous points on eachimage of a stereo pair of images;

FIG. 4 shows schematically the formation of the right eye viewing windowin front of an autostereoscopic 3D display;

FIG. 5 shows schematically the formation of the left eye viewing windowin front of an autostereoscopic 3D display;

FIG. 6 shows in plan view the generation of viewing zones from theoutput cones of a 3D display;

FIG. 7 shows one window profile for an autostereoscopic display;

FIG. 8 shows a schematic of the output profile of viewing windows froman autostereoscopic 3D display;

FIG. 9 shows another schematic of the output profile of viewing windowsfrom an autostereoscopic 3D display;

FIG. 10 a shows an autostereoscopic display comprising a lenticular lensarray aligned at a tilted angle to a pixel array;

FIG. 10 b shows a modified pixel structure to improve the AIU of thedisplay of FIG. 10 a;

FIG. 11 a shows in cross section liquid crystal alignment in a radiallysymmetric mode spatial light modulator;

FIG. 11 b shows in cross section liquid crystal alignment in anotherradially symmetric mode spatial light modulator;

FIG. 12 shows in plan view liquid crystal alignment in a radiallysymmetric mode spatial light modulator;

FIG. 13 a shows in cross section a switchable lenticularautostereoscopic display is using a spatial light modulator of FIGS. 11and 12;

FIG. 13 b shows in cross section a switchable parallax barrierautostereoscopic display using a spatial light modulator of FIGS. 11 and12;

FIG. 14 shows a Poincare sphere interpretation of polarizationmodulation in a radially symmetric mode spatial light modulator;

FIG. 15 a shows an arrangement of lenticular screen and pixel array;

FIG. 15 b shows a further arrangement of lenticular screen and pixelarray;

FIG. 15 c shows a further arrangement of lenticular screen and pixelarray;

FIG. 15 d shows a further arrangement of lenticular screen and pixelarray;

FIG. 16 a shows the AIU and ACU properties of a prior art landscapepixel autostereoscopic display;

FIG. 16 b shows the AIU and ACU properties of a prior art portrait pixelautostereoscopic display;

FIG. 17 shows a pixel arrangement embodiment of the present invention;

FIG. 18 a shows a layout of circuitry for a pixel arrangement embodimentof the present invention;

FIG. 18 b shows a further layout of circuitry for a pixel arrangementembodiment of the present invention;

FIG. 19 shows a detail of a pixel arrangement embodiment of the presentinvention;

FIG. 20 shows a detail of a pixel arrangement embodiment of the presentinvention;

FIG. 21 shows a detail of a pixel arrangement embodiment of the presentinvention;

FIG. 22 shows a detail of a pixel arrangement embodiment of the presentinvention;

FIG. 23 shows a pixel arrangement embodiment of the present invention;

FIG. 24 shows a further pixel arrangement embodiment of the presentinvention;

FIG. 25 shows a further pixel arrangement embodiment of the presentinvention;

FIG. 26 shows a further pixel arrangement embodiment of the presentinvention;

FIG. 27 shows a further pixel arrangement embodiment of the presentinvention; and

FIG. 28 shows a further pixel arrangement embodiment of the presentinvention.

DETAILED DESCRIPTION

FIG. 10 a shows one known arrangement of a lenticular screen alignedwith a pixel array to provide an autostereoscopic display apparatus. Thelenticular screen 172 comprises slanted elongate lenticular elementsarranged over and aligned to a spatial light modulator 170 comprising anarray of pixels 62 each comprising in this example a single aperture.The individually addressable pixels 62 are of different colors and arearranged with a repeating unit of pixels that repeats in a horizontalrow direction and in a vertical column direction. Thus the opticalelements of the lenticular screen 172 have geometric axes extending inparallel across the spatial light modulator in a direction inclined atan angle with respect to the column direction which in this case is thevertical direction. For example the pixels comprise columns 65 of redpixels, columns 67 of green pixels and columns 69 of blue pixels.

A lenticular screen is a type of parallax element that may comprise anarray of vertically extended cylindrical microlenses and directs lightfrom the pixels into different viewing windows. The term “cylindrical”as used herein has its normal meaning in the art and includes not onlystrictly spherical lens shapes but also aspherical lens shapes. Thepitch of the lenses again corresponds to the viewpoint correctioncondition so as to provide viewing windows at the correct viewingdistance. The curvature of the lenses is set substantially so as toproduce an image of the LCD pixels at the window plane. As the lensescollect the light in a cone from the pixel and distribute it to thewindows, lenticular displays have the full brightness of the base panel.

A cylindrical lens describes a lens in which an edge (which has a radiusof curvature) is swept in a first linear direction. The geometric axisof the cylindrical lens is defined as the line along the centre of thelens in the first linear direction, i.e. parallel to the direction ofsweep of the edge 71. Notional lines parallel to the geometric axis arecalled ray lines 64. The overlap (or intersection) of the notional rayline 64 with the pixel aperture 62 provides information relating to theangular intensity uniformity and angular contrast uniformity propertiesof the display.

Thus the overlap 72 of one ray line 64 with a pixel aperture 62 of thecolumn of pixels 65 may have the same length or size as that of theoverlap 66 of the ray line 64 with the pixel aperture 62 of the columnof pixels 67 at the equivalent position, wherein the column of pixels 67is adjacent to the column of pixels 65. However, this overlap 72 may bedifferent from the overlap 68 of a ray line 64 at a different positionacross the pixel aperture 62. In fact, the total overlap between thepixel apertures 62 can typically be considered by investigating theoverlap between any two laterally adjacent pixel apertures 62 for onesingle ray line 64. Thus the total overlap is given by the summation ofoverlaps 68 and 70.

The plot of overlap line length zeta (ζ) 73 across ray line position y49 relative to pixel position in the pixel apertures 62 is termed thezeta (ζ) function 75. As can be seen in FIG. 10 a, the rectangular pixelapertures 62 provide a peak 74 of increased intensity. When imaged tothe viewing window plane 42 by the lenticular screen, this results in anincreased window intensity at certain viewing positions. Thus, as anobserver moves across the viewing window plane 42, the intensity of thedisplay will vary causing image flicker. Such an artefact is undesirableas the eye is very sensitive to such levels of flicker. For example, anintensity artefact of less than 0.5%-5% in the integrated intensity (orluminance) function 60 may be visible to a moving observer. It is thusdesirable to reduce this effect as much as possible by providing a highuniformity zeta (ζ) function (intensity function) 75.

One known means to improve the zeta uniformity is shown in FIG. 10 b. Inthis case, the peaks 74 of zeta (ζ) (notional ray line overlap withpixel aperture function) are minimized by rectangular cut-outs 76. Thusthe AIU will have high uniformity. As will be shown, such a techniquedoes not provide high AIU for radially symmetric liquid crystal modes.Further, as will be shown below, such a technique does not compensatefor angular contrast uniformity (ACU) effects.

In autostereoscopic displays that use slanted lenses, the angle of thenotional ray line with respect to the rows and columns of pixels may bedetermined by considering various desired properties of the 3D image fora given arrangement of color pixels. For example, with pixels in whichthe red, green and blue pixels are of equal size and together form asquare color pixel unit cell with size 3 units horizontally and 3 unitsvertically, a ray line that is at an angle of 1 unit horizontally and 3units vertically has an angle of 18.43 degrees to the vertical andprovides windows which overlap to a first extent. Reducing the angle to9.46 degrees by setting the ray line with an angle of 1 unithorizontally and 6 units vertically increases the overlap betweenadjacent windows (broadens the base of the triangular window structureof FIG. 9). Broader windows will show increased view overlap so thatundesirably pseudoscopic images are more likely to occur, as well asincreasing the amount of blur in images. However, such an image willvary more smoothly as an observer moves laterally with respect to thedisplay as well as having a greater vertical viewing freedom compared tothe angle of 18.43 degrees. The two different angles also provide pixelswith different spatial frequency information which can modify thefidelity of the 3D image. Alternative angles are also possible with thedisplay properties modified as required.

In general, the ray lines (i.e. geometric axes of the optical elements)are inclined at an angle such that displacement of the geometric axes inthe row direction by the pitch of the pixels in the row direction occurswithin the pitch of the pixels in the column direction multiplied by anon-zero integer. For example, where the column direction isperpendicular to the row direction, this means that the geometric axesof the optical elements are inclined with respect to the columndirection at an angle equal to arctan(pr/(pc·n)), where pr is the pitchof the pixels in the row direction, pc is the pitch of the pixels in thecolumn direction, and n is a non-zero integer. The angles of 18.43degrees and 9.46 degrees mentioned above correspond to the cases that nis 1 or 2, respectively.

The spatial light modulator is a radially symmetric mode liquid crystaldisplay device comprising an array of pixels arranged in rows andcolumns (as shown in more detail below) providing radially symmetricalignment of the molecules of liquid crystal. FIG. 11 a shows in crosssection of part of an example of such a radially symmetric mode tospatial light modulator. A liquid crystal layer is sandwiched betweensubstrates 100, 102. The liquid crystal molecules 110 are aligned withtilted director orientation 114 by bump features 104 that protrude intothe liquid crystal layer from the substrate 100. Between adjacent bumpfeatures 104, 105 the liquid crystal directors are required to undergorelatively discontinuous tilts, thus causing disclinations in thealignment. Such disclinations cause scattering that degrade imagecontrast. Light blocking layers 108 and 106 shield regions of liquidcrystal disclinations and addressing electronics to optimise displaycontrast.

The bump features 104, 105 are a type of alignment feature that providesa radially symmetric liquid crystal alignment. Such an alignment may beproduced by bump features 104, 105 that are physical bumps as shown inFIG. 11 a. However the radially symmetric alignment may be produced inother manners by other types of alignment feature, such as by a changein the alignment layer properties without the need for a physical bump,as shown for example in FIG. 11 b. FIG. 11 b shows in cross sectionliquid crystal alignment in another radially symmetric mode spatiallight modulator. In regions 112, the alignment properties are differentto region 111 so that the resultant alignment away from the region 111is substantially the same as shown in FIG. 11 a away from the bumpfeature 104. The region 111 is thus a different form of alignmentfeature.

The alignment feature may also be produced by an electrode pattern or apyramid shape for example, but still produce an essentially radiallysymmetric liquid crystal alignment. In this specification the term“alignment feature” is defined to include the above options eithersingularly or in any combination. In each case, a further light blockinglayer or partial light blocking layer may be incorporated in the regionof the alignment feature to remove the visibility of alignment defectssuch as disclinations.

In plan view of a single pixel 118 as shown in FIG. 12, the single pixel118 has two apertures 116, 117 for example, but not limited herein. Thebump features 104, 105 may be circular and the light blocking layer 106may comprise apertures 116, 117 each comprising a single bump feature104. The liquid crystal molecules take a radially is symmetric alignmentat the bump features as shown. The pixel 118 with apertures 116, 117 isaddressed with a single addressing voltage so that the driving of theliquid crystal molecules in each sub-aperture is typically identical.Thus addressable pixels that comprise multiple bump features comprisemultiple pixel apertures to reduce the effects of scatter.

Across the area of each of the apertures 116, 117, the liquid crystalmolecules are arranged with a set of tilts as a result of the alignmentof the liquid crystal molecules at the surface of the bump and thepropagation of the alignment across the pixel aperture. As will bedescribed with reference to FIG. 14, each tilt contributes to anoptimized contrast at a particular viewing angle. In the 2D mode ofoperation, the summation of the contribution from each tilt contributesto a more uniform viewing mode than for example the twisted nematic (TN)mode in which a single tilt is present across the whole of the pixel.Thus, in the 2D mode of operation, radially symmetric modes have ahigher uniformity of contrast with viewing angle than TN mode devices.As will be shown, this property is not preserved when a conventionalradial symmetric mode LCD is combined with an elongate parallax opticsuch as a parallax barrier or lenticular screen.

FIG. 13 a shows in schematic side view of an autostereoscopic displayapparatus similar to those described in WO-03/015424 comprising aswitchable lenticular element. The autostereoscopic display apparatuscomprises a backlight 120, a polarizer to 122, a quarter waveplate 124,(array) substrate 102, pixellated liquid crystal layer 128, (opposite)substrate 100, quarter waveplate 132, polarizer 134, substrate 136,switchable polarization rotating layer 138, substrate 140, birefringentmicrolens array 142 (comprising a lenticular screen), isotropic layer144 and substrate 146. Such a 2D/3D display is capable of switchingbetween an autostereoscopic 3D display and a full resolution 2D displaywith full brightness in 2D and 3D modes. Alternatively the switchablebirefringent lens and polarization switching apparatus may be replacedby a fixed lens so that the display is a non-switching 3Dautostereoscopic display.

FIG. 13 b shows a parallax barrier autostereoscopic display apparatus. Aparallax barrier is an alternative form of parallax element to alenticular screen that directs light into different viewing windows. Theswitchable lenticular screen of FIG. 13 a is replaced by a liquidcrystal parallax barrier element comprising substrates 125, 129;patterned liquid crystal layer 127 and output polarizer 131. Theparallax barrier operates in a similar way to a lenticular screen withthe pixel arrangements of the present invention, although has lowerthroughput efficiency. Alternatively, the parallax barrier may be afixed barrier. The geometric axis of the parallax barrier is againparallel to the optical axis of the optical elements that are theapertures in the parallax barrier.

FIG. 14 shows the operation of the pixel of FIGS. 11 and 12. Incidentlight from backlight 120 is polarised by polarizer 122 to provideincident polarization state 150 (for example 0 degrees) and is convertedto right circular polarization state 152 by the quarter waveplate 124.Each orientation of the liquid crystal molecules then provides a halfwaveplate function so that in the unswitched state the light isconverted to left circular polarization state 158. For example a liquidcrystal molecule 110 indicated by the line 164 provides a rotation aboutan axis so that the transition 166 is provided on the Poincare sphere.Each orientation provides a transition 160, 162 or 166 at a differentorientation. Following the quarter waveplate 132 provides transition 162to provide an output polarization state 156 which is transmitted orabsorbed by the output polarizer 134. In the opposite drive state, themolecules are aligned so as to provide substantially no phase modulationso that the polarization state at the input to the polarizer 134 issubstantially parallel to the input polarization state 150.

Advantageously such an arrangement provides enhanced angular contrastproperties of the display (wide viewing angle) compared to twistednematic modes of operation.

FIG. 15 a shows a first arrangement of a display pixel plane 170 with alenticular screen 172. Pixels are arranged in an array 174 with columnsand rows with the rows substantially parallel and perpendicular to thegeometric axis of the lenticular lens elements. The pixels have aportrait pixel aperture orientation. In FIG. 15 b, the pixel array 176has pixels with a landscape orientation. In FIG. 15 c, the lenticularscreen 172 is inclined at a non-zero angle 176 with respect to thearrangement direction (vertical) of the rows of pixels of the array 174.In FIG. 15 d, the lenticular screen 172 is vertical but inclined at anon-zero angle 176 with respect to the arrangement direction of the rowsof the pixels of the array 174. The arrangement of FIG. 15 dadvantageously produces vertical viewing windows so that the optimumviewing position does not appear to change as the viewer movesvertically with respect to the display. In these examples, the rows andcolumns of pixels are perpendicular, although in the general case thisis not essential and the row direction and column direction may bearranged at an angle of less than 90 degrees.

FIG. 16 a shows the landscape pixel arrangement of FIG. 15 b whencombined with an array of pixels 118 of FIG. 12. Two columns of pixelsare placed under each lens of the lens array to provide a two viewautostereoscopic display with vertical lenses. The lenticular screen 172has vertical notional line (ray lines 64) parallel to the geometric lensaxis. Light from the spatial light modulator is collected from a givenray line 64 and directed in a particular direction. The light receivedby a viewers eye may be analyzed by considering an intensity (orluminance) profile or ‘spot size’ sigma (σ) function 182 representingthe image of a notional observer's pupil at the pixel plane produced bythe lenticular screen 172, sigma (σ) 180 against position at the pixelplane, y 49. The viewer's eye receives light collected from this image.

The zeta (ζ) function 185 representing the distribution of the overlapsof the notional ray lines 64 with the apertures 116, 117 is shown. Inparticular this has troughs 181, of zero zeta (ζ) peaks 179 of maximumzeta (ζ) and dips 183 representing the zeta (ζ) function at the bumpfeature 104 regions.

When the pixels 118 are imaged by the lenticular screen 172 to theviewing window plane, for example as shown in FIG. 6, the variation ofintensity (alpha (α)) 50 against position x 51 at the viewing windowplane is given by the function 184 as shown, being the convolution ofthe sigma (σ) function 182 with the zeta (ζ) function 185. This AIUvariation means that the intensity varies as the eye moves across thewindow plane. If the spot size sigma (σ) function 182 is increased, thenthe window may be blurred to have less AIU variation as shown by thealpha (α) function 186. However, such a blurring serves to increase thecrosstalk characteristics of the display, thus degrading the 3D imagequality.

This analysis can be further extended to evaluate the angular contrastuniformity (ACU). The contrast xi (ζ) 188 is shown schematically againstposition y 49 across the pixel plane. It can be seen that for a singleaperture 117 or 116 there are various different contrast xi (ζ)functions 190, 192, 194 across the aperture 117 or 116. In regions 191,the xi (ζ) 188 is zero so the contrast is indeterminate and marked aszero. Each xi (ζ) function 190, 192, 194 represents a different polarcoordinate of viewing the output of the display. Thus the contrastdirectly on-axis may be represented by one xi (ζ) function 194, whilethe contrast at polar coordinate viewing the display from 45 degrees offnormal in the north-east direction may be represented is by a differentfunction 192.

The convolution of the spot function sigma (σ) function 182 with thecontrast xi (ζ) functions 190,192, 194 together with the collection coneangle of the lenticular screen provides the angular contrast beta (β)196 against window position x 51. It can be seen that each viewing anglehas a different contrast beta (β) functions 198, 200, 202, eachcorresponding to contrast variation as the eye moves across the windowplane, the contrast variation being different for different viewingangles. Thus the angular contrast uniformity ACU is not uniform acrossthe output of the display.

Angular contrast uniformity, ACU can manifest itself as intensitychanges in black states of the display, and can thus result in flickereffects in the black states of the display as the observer moves.Further such an effect can be manifested as color changes across thewindow plane due to the variation of chromaticity of the liquid crystalhalf-wave plate effect for any particular liquid crystal molecule tilt.

Such effects will vary with polar viewing angle. For ease ofexplanation, the variation from a single polar observation coordinatewill be described in further ACU functions (xi (ζ) against y and beta(β) against x) in this specification.

FIG. 16 b shows the arrangement of portrait pixels of FIG. 12 with alenticular screen. In this case, both bump features 104, 105 are alignedso that there is a single contrast variation per viewing window ratherthan the double contrast variation as shown in FIG. 16 a.

Embodiments

FIG. 17 shows a first embodiment of the present invention. Radiallysymmetric mode portrait pixel 210 comprises a top aperture (or so-calledtop or first displaying area) 214 and bottom aperture (or so-calledbottom or second displaying area) 216, each containing a bump feature104 arranged as described above to provide radially symmetric alignmentof the molecules of liquid crystal. FIG. 17 shows three pixels 210 ofdifferent colors, for example red, green and blue. The apertures 214 and216 of the pixels 210 are separated by regions 218 containingelectrodes, capacitors and other addressing circuitry. As described infurther detail below, each pixel 210 is individually addressable, thatis each pixel is addressable separately from each other. The topaperture 214 and bottom aperture 216 of each pixel 210 may beaddressable unitarily or may be addressable separately.

The apertures 214 and 216 are shaped in a particular manner havingregard to the bump feature 104 to improve AIU and ACU. Aperture 214 hasa horizontal top edge 215, inclined edges 217, 219 and a bottom edge 221with bump feature compensation feature 220. The bottom edge 221 and thebump feature compensation feature 220 are integrated. The lower aperture216 has the same aperture shape, rotated through 180 degrees. In thisexample, the bump feature compensation feature 220 is aligned with thebump feature 104 parallel to (with respect to) the ray lines 64 and hasan aperture shape arranged to compensate for the loss in the bumpfeature region 104 as will be described with reference to FIGS. 19-22.

The edges 217 of the apertures 214 and 216 of a single pixel 210 overlapin overlap region 225 and the edges 219 of the apertures 214 and 216 oftwo adjacent pixels 210 overlap in overlap region 227. Ignoring the bumpfeature compensation feature 220, the top edge 215 and bottom edge 221are parallel so that the apertures 214 and 216 outside the overlapregions 225 and 227 have the same height parallel to the ray lines 64.In this example, areas of the apertures 214 and 216 inside the overlapregions 225 are substantially the same and/or substantially align withrespect to the ray lines 64. Similarly, in the overlap regions 225, 227,the edges 217 are parallel to each other and each inclined with respectto the ray lines 64, and the edges 219 are also parallel to each otherand each inclined with respect to the ray lines 64.

As a result, ignoring the bump feature compensation feature 220, thetotal length of intersection of a ray line 64 with the pixels 210 in asingle row is the same for each position of the ray line 64 (being anotional line). Outside the overlap regions 225 and 227, theintersection is with a single one of the apertures 214 and 216 and thelength of intersection is the distance between edges 215 and 221. In theoverlap region 225, this length of intersection is summed over twoapertures 214 and 216 of the same pixel 210. In the overlap region 227,this length of intersection is summed over two apertures 214 and 216 ofdifferent pixels 210 that are different colors. Considering pixels 210of a single color, the total length of intersection of a ray line 64with the pixels 210 of the same color that are adjacent along the rayline 64 is the same for each position of the ray line 64 (being anotional line). For positions outside the overlap regions 225 and 227and positions in overlap region 225, the ray line 64 has a constantlength of intersection with a pixel 210 in a single row shown in FIG.17. This accounts to the greatest range of positions of the ray line 64.However, for positions in overlap region 227, the length of intersectionwith a single pixel 210 of a single color in a single row is less, andreduces as the ray line 64 moves outwardly. However, in subsequent rows,the colors of the pixels 210 are offset. This has the result that in theoverlap region 225 the intersection with the pixel 210 in the row shownin FIG. 17 sums with the intersection with a pixel 210 of the same colorin another row that is adjacent along the ray line 64, so that the totallength of intersection with pixels 210 of that color remains the same.

Thus ignoring the bump feature 104 and bump feature compensation feature220, the shape of the apertures 214 and 216 provides a uniform zeta (ζ)function (intensity function) 75 for all positions y 49 of the ray lines64.

The bump feature compensation feature 220 is arranged to compensate forthe is bump features 104, providing a uniform zeta (ζ) function 75 eventaking into account the bump features 104. As described further belowwith reference to FIGS. 19 to 22, this is achieved by the bump featurecompensation feature 220 being shaped such that the total length ofintersection of a ray line 64 with the pixels 210 of a given color,weighted for the intensity at the bump feature 104, is the same for eachposition of the notional ray line 64.

The shape of the apertures 214 and 216 including bump featurecompensation features 220 has several important benefits.Advantageously, the AIU of the display is constant independent of thespot sigma (σ) function 182. Typically the spot sigma (σ) function 182varies with angle due to the aberrations of the lens so that the alpha(α) function 186 and thus the AIU varies with viewing angle. However,the current embodiments mean that the change in spot sigma (σ) function182 with viewing angle is not visible as the observer changes viewingposition. Such a display shows reduced flicker to an observer movingwith respect to the display.

Further, the tolerance on manufacture of the optical elements can berelaxed so that the optical elements are cheaper to manufacture. Furtherthe 2D mode performance can be enhanced because errors in the componentperformance (such as scatter or refractive index mismatch) are notvisible as 2D AIU errors.

Further, the spot size of the optical elements can be reduced so thatthe level of cross talk between adjacent views can be reduced, thusincreasing 3D image quality. Further, the amount of blur betweenadjacent images can be reduced in multi-view displays so that the amountof depth that can be shown increases.

Further, the window size of a two view display can be increased so thatwider viewing windows can be used. For example, such an arrangementenables nominal window sizes at the viewing window plane of 130 mmrather than 65 mm. The small overlap between the adjacent pixel columnsmeans that the region of cross talk between the views is minimizedcompared to the prior art. Thus the observer can have a wide region inwhich an orthoscopic image can be seen. If the observer moves laterally,a 2D image is seen (as both eyes are in the same viewing window) beforea pseudoscopic image is seen. Such a display has an extendedlongitudinal viewing freedom.

It can further be seen that the position of the bump features 104 in thetwo apertures 214 and 216 of a pixel 210, and hence the bump featurecompensation features 220, are offset in the direction perpendicular tothe ray lines 64, rather than being vertically aligned as in a 2 viewdisplay using portrait pixels 118 of the form shown in FIG. 12. Thus theray lines 223 through the centre of the regions of the bump features 104can be seen to be distributed across the pixel width. The spacing of theray lines 223 may be equal. In this manner, the bump feature 104 providecompensation for ACU effects in the display providing a more uniform ACUfunction 226 than otherwise possible. As the bump features 104 provideradially symmetric alignment of the molecules of the liquid crystal, ingeneral terms ray lines 64 at different positions cross molecules of theliquid crystal that are aligned differently, depending on the positionof the ray line 64 with respect to the bump features 104. The differentalignment causes variation in the contrast of the light collected fromthe different notional lines and observed by a viewer at a correspondingviewing position, hence generating ACU. The ACU is poor in the pixelarrangement shown in FIG. 16 a, but this effect is reduced by the bumpfeatures 104 being offset in the pixel 210. This is because, across therange of possible positions of the notional lines, there is a reductionin the overall variation in the alignment of molecules of liquid crystalthat causes variation in contrast.

Thus embodiments provide enhanced AIU and enhanced ACU in radiallysymmetric mode displays. Such displays show low levels of flicker as theobserver moves and show increased tolerance to manufacturing errors ofoptical components and are thus of lower cost.

Advantageously, the embodiments provide a uniform variation of intensitywith viewing angle of the autostereoscopic display. Such embodimentsremove residual visibility of the black mask between the domains of thedisplay. An observer looking at the display sees a uniform intensitystructure across the display for a wide range of viewing angles. Thus,the display does not appear to flicker as the observer moves withrespect to the display. Such flicker is a disturbing visual artefact.Further, the cost of the pixel arrangement is substantially the same asthe known pixel arrangements. Thus, the AIU of the display asrepresented by the function 60 is advantageously substantially constantfor all angles of viewing of the display, regardless of the focalcondition of the parallax element. Such an arrangement advantageouslyalso provides high ACU. Thus, the variations of contrast or color of thedisplay are minimized as the observer moves their head. If the contrastwere to change as the observer moves, then the images would also appearto flicker in intensity or color, degrading display performance.

In switchable 2D/3D displays, there may also be some residual 3Dfunction when the display is switched to 2D. Advantageously, in thepresent embodiments, the AIU and ACU are independent of the focalcondition of the parallax optic. Thus, if there is some residual 3Dfunction in the 2D mode, advantageously it will not be manifested as AIUor ACU effects in the present embodiments. This enables themanufacturing tolerances of the optical elements to be relaxed. Forexample, in switchable birefringent lenses, as described for example inU.S. Pat. No. 7,058,252, there may be some residual refractive indexstep between a liquid crystal and isotropic lens material. Inconventional pixels, this may cause an AIU error due to the residuallens function. In the present embodiments, the tolerance on index stepcan thus be relaxed, advantageously reducing lens cost and increasingyield and a wider choice of materials and wider processing latitude.

In the present embodiments, the actual alignment of the individualdomains can be adjusted to optimize aperture ratio while providingsufficient room for electrodes and addressing circuitry. The figures areprovided for illustrative purposes, but could be adjusted.

Further, in the 3D mode, the focus of the lens can be optimized, ratherthan defocussed as reported in prior art systems. Advantageously thisresults in an increased separation of view data across adjacent viewingwindows. Reducing window overlap advantageously reduces the blur seen in3D images so that the total amount of depth that can be shown isincreased. Further, the pseudoscopic image intensity can be reduced,increasing display comfort. Such an arrangement can be applied to 3Ddisplays using parallax optics such as lenticular screens and parallaxbarriers.

Further in lenses which have a variation in optical function withviewing angle such as caused by off-axis aberrations or by changes inthe effective lens index step with incident illumination angle, theregion of light collected from the pixel plane will vary with viewingangle. In the present embodiments, advantageously, the ray line has aconstant intersection length for all ray lines for pixels of the samecolor along the ray line which means that as the region from which raylines are collected varies with viewing angle, the same intensity andcontrast function will be produced. Such a pixel arrangement thereforeenables high viewing angle without the generation of non-uniformintensity distributions giving good AIU and ACU properties.

Further, in passive birefringent lenses with performance dependent onthe viewing angle of a polarization switcher, the intensity variationwill be independent on the polarization output of the switcher. Such anarrangement enables the switcher to have reduced optical compensationfilms, and so is cheaper, thinner and easier to manufacture.

Further in active birefringent lenses which have a 3D function off-axiswhen the lens is arranged in the 2D mode, the black mask is not resolvedas a change in AIU or ACU with viewing angle.

Thus the present embodiments have advantages of increased image qualitycombined with reduced cost without compromising the 2D performance ofthe display. Such an arrangement is achieved by modification of layoutof pixel apertures.

FIG. 18 a shows one possible layout of the pixels 210 shown in FIG. 17in which the edges 219 between the columns of pixels are sloped(inclined). Each pixel 210 is individually addressable as follows.Apertures (displaying areas) 214, 216 are driven by column electrodes250, row electrodes 252, transistor elements 254 and electrode 256. Apixel region is formed with two adjacent row electrodes 252, twoadjacent column electrodes 250. The electrode 256 is in the pixelregion. Electrodes 256 and the opposite electrode (not shown) of theopposite substrate may form a capacitor for keeping an electric field tothe liquid crystal layer located therebetween. As shown in FIGS. 18 aand 18 b, two apertures 214 and 216 are in the pixel region. However, itis not limited herein. There may be only one or more than two aperturesin a single pixel region. In this manner, the addressing circuitry canconveniently be positioned between the respective pixel apertures whileretaining the pixel aperture functions. Further, some vertical overlapof pixels is possible so that the aperture ratio of the system can beoptimized FIG. 18 b shows a further possible layout of the pixels shownin FIG. 17 in which the edges 219 between the columns of pixels arevertical, so aligned substantially parallel with the geometric axes ofthe parallax optical element. This arrangement has a lower apertureratio but advantageously has a lower cross talk region between the viewscompared to FIG. 18 a.

Detail of the bump feature compensation features will now be describedby illustrative embodiments. The bump features 104 when analyzed byquarter waveplates and polarizers comprise regions of lower intensitythan the surrounding pixel. Thus, the intensity of the ray line overlapmust be considered in addition to its length. The intensity of the bumpfeature 104 needs to be included to provide a uniform zeta (ζ) 73 for aparticular position y 49 in the pixel plane. Thus, the pixel apertures214, 216 are shaped so that the length of intersection that is equalizedfor different positions of the ray line 64 is a weighted length ofintersection. That is, across the bump feature 104, the length ofintersection is weighted for the intensity of the light modulated by thebump feature 104 as a fraction of the intensity of light modulated bythe remainder of the pixel 210, i.e. the remainder of the pixel otherthan the bump feature 104.

By way of example, FIG. 19 shows a case in which the intensity of theoutput in the region of the bump feature 104 is uniform and 50% of theintensity of the output in the remainder of the pixel 210. In order tomaintain the ray line 64 overlap, along the ray lines 64, the length 224of the bump feature compensation feature 220 (in a direction parallel tothe ray lines 64) is smaller than that of the length 222 of the bumpfeature 104 (in a direction parallel to the ray lines 64), for example,a half of the length 222 of the bump feature 104. As the intensity inthe bump feature compensation feature 220 is twice that of the bumpfeature region 104, then the total ray line intensity is constant acrossthe width of the pixel.

FIG. 20 shows a case in which the bump feature 104 has zerotransmission. In this case, the tab length 224 is the same as the length222 of the bump feature 104.

In other embodiments, the intensity function may vary across thelength/width of the bump feature 104. In this case, the length 224 ofthe bump feature compensation feature 220 in a direction parallel to theray lines 64 is set, at each position of the ray line 64, on the basisof the integral of the intensity function over the bump feature 104 atthe respective position of the ray line 64 for compensating the lightwhich is blocked by the bump feature 104. This has the result that theweighted length of intersection with the ray line 64, and hence the zeta(ζ) function, are substantially constant at each position of the rayline 64.

In FIG. 21, the bump feature compensation features 228 and 220 are shownas distributed at the top and bottom of the aperture 214.Advantageously, such an arrangement may provide for a differentarrangement of addressing electronics, increasing the overall apertureratio. In FIG. 22, the bump feature compensation feature 228 is combinedwith the shape of the inclined edge. That is to say, the inclined edgeis connected with the edge of the bump feature compensation feature 228as shown in FIG. 22.

It is further the purpose of embodiments to provide enhanced ACUproperties by providing a spatial frequency of bump features and bumpfeature compensation features across the pixel width greater than thepixel spatial frequency when added across adjacent rows. In this manner,variations in ACU of a display can be minimized.

Of course the pixels may provide this effect with shapes other than thatshown in FIG. 17. Examples of other shapes will now be described. FIGS.23 to 26 show various embodiments of landscape radially symmetric modepixels with bump feature compensation features and more than one bumpfeature across a pixel width summed across at least two adjacent rows ofpixels.

FIG. 23 shows an example of four rows 264 to 270 of pixels, eachcomprising a single aperture having a bump feature compensation feature220 and bump feature 260 and 262 over two adjacent rows of pixels. Theadjacent rows may be pixels of different colors. For example, rows 264,270 may be red pixels, row 266 may be green and row 268 may be blue.Considering pixels of a single color, the total length of intersectionof a ray line 64 with the pixels of the same color that are adjacentalong the ray line 64 is the same for each position of the ray line 64(being a notional line). Considering the rows 264, 270 of red pixels,for some positions of the ray line 64, the ray line 64 intersects with apixel in only one row 264 or in only the adjacent row 270, and at thesespositions the pixels have a constant height so that the length ofintersection is equal to that height. At other positions of the ray line64, the pixels in the adjacent rows 264 and 270 overlap along the rayline 64 with correspondingly tapered shapes so that the total length ofintersection summed over the pixels in the adjacent rows 264 and 270substantially remains the same.

Thus, for pixel rows of the same color, bump features 262 and 272 arealso laterally spaced to provide more than one bump feature compensationfeature across a pixel width summed across at least two adjacent rows ofpixels of the same color. The ACU improves, because the horizontallyaligned liquid crystal directors in one row are aligned with verticallyaligned liquid crystal directors in an adjacent row, thus averaging therespective contrast properties across the two rows. In the region ofoverlap between two pixel apertures along a vertical ray line, the edgesof the pixel apertures may be inclined such that across any two rows ofpixels, the length of intersection of a ray line may be constant for allpositions of the ray line. In the centre of the pixel width (rather thanaperture width), the inclination angle from the vertical may be greaterthan at the edge of the pixel width. This is because the overlap of thepixel apertures should be minimized in the region in which the view datachanges in the viewing window plane; however in the centre of the pixelwidth, the higher inclination angle from the vertical may enable moreconvenient routing of row electrodes.

FIGS. 24 to 26 show examples similar to FIG. 23 but with the pixelssplit to comprise two apertures each containing a bump feature.

FIG. 24 similarly comprises three bump features 274, 276 and 278laterally spaced across two rows of the same color. Liquid crystaldisclinations are present in regions between the bump features 274, 276so an additional masking area 275 is inserted to remove visibility ofthe disclinations. This further requires modification of the pixelboundaries in order to maintain the zeta (ζ) function uniformity. Inthis example, the edges of the apertures are inclined with respect tothe vertical which achieves a greater aperture ratio than for verticaledges in which the pixels are vertically offset as will be shown in FIG.27. Increasing the number of bump features thus improves the ACU.Similarly FIGS. 25 and 26 show four bump features 280, 282, 284, 286averaged across two adjacent rows of the same color. Varying the bumpfeature position may be extended over more than two rows. As shown inFIG. 25, the bump features 286 do not necessarily have to appear in thepixel aperture.

FIG. 27 shows a further arrangement of pixel apertures and bump featurecompensation features for use in a two view display with verticallenses. Pixel columns 288, 289 are under a first lens of the lens array172 while pixel column 290 is under the adjacent lens of the lens array172. The pixels are arranged in a group of four rows 291, 292, 293, 294.Apertures 295, 296 and 297 have a width of half of the pixel pitch whileaperture 298 has a width of quarter of the pixel pitch. The lateralposition of the bump feature 104 in each of the apertures 295, 296 and297 is different so as to provide a more uniform ACU as will bedescribed. The length of the pixels in a direction parallel to the raylines 64 is substantially constant other than in the bump feature 104and bump feature compensation feature 220 for reasons explainedpreviously. Alternatively, the pixel edges may be sloped and overlappingso that the zeta (ζ) function is constant. Within the group of rows thetotal ray line 299 overlap at any position across the aperture isconstant at two pixel aperture lengths in a direction parallel to theray lines 64. Advantageously, this arrangement provides a regularsequence of bump features 104 as shown by the sequence of ray lines 300.Thus such an arrangement has a good ACU performance as well as good AIUperformance in radially symmetric mode devices.

The embodiments of the invention described hereinbefore comprisevertical lenses and vertical columns of pixels. However, the presentinvention can be applied to several different configurations includingthose shown in FIG. 15 a to FIG. 15 d for both lenticular screens andparallax barriers. FIG. 28 shows a further embodiment in which thelenses are tilted with respect to an array of substantially radiallysymmetric mode pixel apertures 301 and 303 in a manner similar to FIG.15 c. In this case, the bump feature compensation features 302, 304 arelaterally offset with respect to the bump feature regions 305 along theray line 64 parallel to the geometric lens axis. Further rectangularcutout sections are shown to improve AIU. The shape of the bump featurecompensation features 302, 304 are modified from semi-circles shownpreviously so as to provide zeta (ζ) function 306 uniformity and furtherto minimise xi (ζ) function 308 uniformity. Advantageously the AIU andACU of slanted lens multiview displays can be enhanced, while increasing3D and 2D image quality and reducing the cost of the optical componentsfor the reasons described above.

Throughout this description, the pixel aperture may be defined by asingle layer such as the black mask layer formed by the light blockinglayers 106 and 108. Advantageously, such an arrangement providesimproved tolerance to manufacture compared to structures in which thepixel aperture is defined by multiple layers. The position of the bumpfeature 104 however will be defined by a separate layer compared to theblack mask layer. In this case, the alignment of the black mask duringassembly is advantageously set to be laterally aligned with the bumpfeature 104. Advantageously, the layer comprising the bump features 104may be positioned on the same substrate as the black mask layer.

1. An autostereoscopic display apparatus comprising: a spatial lightmodulator having an array of individually addressable pixels ofdifferent colors arranged in rows and columns, each pixel comprising atleast one aperture that contains liquid crystal and has an alignmentfeature arranged to provide radially symmetric alignment of themolecules of the liquid crystal; and a parallax element comprising anarray of optical elements arranged over the spatial light modulator todirect light from the pixels into different viewing windows, the opticalelements having geometric axes extending in parallel across the spatiallight modulator transversely to said rows in which the pixels arearranged; wherein the apertures are shaped such that a notional lineparallel to the geometric axes of the optical elements has a totallength of intersection with the pixels of the same color that areadjacent along the notional line, which total length of intersection isthe same for all positions of the notional line when the length ofintersection is weighted across said alignment features by the intensityof light modulated by the alignment feature expressed as a fraction ofthe intensity of light modulated by the remainder of the pixel.
 2. Theautostereoscopic display apparatus according to claim 1, wherein eachpixel comprises plural apertures, each of which comprises liquid crystaland a said alignment feature in the liquid crystal, wherein thealignment features of the apertures of each individual pixel are offsetfrom one another in a direction perpendicular to said geometric axes. 3.The autostereoscopic display apparatus according to claim 2, whereineach pixel comprises at least two apertures that overlap in saiddirection perpendicular to said geometric axes.
 4. The autostereoscopicdisplay apparatus according to claim 3, wherein the portions of said atleast two apertures that overlap each have at least one parallel sidethat is inclined with respect to the direction parallel to the geometricaxes of the optical elements.
 5. The autostereoscopic display apparatusaccording to claim 1, wherein pixels that are adjacent one another in arow comprise respective apertures that overlap in said directionperpendicular to said geometric axes.
 6. The autostereoscopic displayapparatus according to claim 1, wherein the intensity of light modulatedby the alignment feature is zero so that the length of intersection isweighted to zero across said alignment features.
 7. The autostereoscopicdisplay apparatus according to claim 1, wherein the alignment featuresare bump features that protrude into the liquid crystal.
 8. Theautostereoscopic display apparatus according to claim 1, wherein thespatial light modulator comprises a layer of liquid crystal containedbetween two substrates.
 9. The autostereoscopic display apparatusaccording to claim 8, further comprising a light blocking layer definingsaid array of pixels in the liquid crystal layer.
 10. Theautostereoscopic display apparatus according to claim 1, wherein saidalignment features are each formed on one substrate.
 11. Theautostereoscopic display apparatus according to claim 1, wherein therows and columns in which the pixels are arranged are perpendicular. 12.The autostereoscopic display apparatus according to claim 1, wherein thegeometric axes extending in parallel across the spatial light modulatorare perpendicular to said rows in which the pixels are arranged.
 13. Aspatial light modulator comprising: a plurality of pixels, eachcomprising: at least one aperture having a first alignment featurecompensation feature; and at least one alignment feature aligning withthe first alignment feature compensation feature with respect to anotional line.
 14. The spatial light modulator according to claim 13,wherein each of the plurality of pixels further comprises a secondalignment feature compensation feature, and the at least one alignmentfeature is aligned with the second alignment feature compensationfeature with respect to the notional line.
 15. The spatial lightmodulator according to claim 13, wherein the aperture contains liquidcrystal.
 16. The spatial light modulator according to claim 13, whereinthe notional line is a horizontal or a vertical.
 17. The spatial lightmodulator according to claim 13, wherein a tab length of the firstalignment feature compensation feature is smaller than or the same as alength of the alignment feature.
 18. The spatial light modulatoraccording to claim 13, wherein the aperture further has: a horizontaltop edge; two inclined edges connected with two ends of the horizontaltop edge, respectively; and a bottom edge, wherein the bottom edge andthe first alignment feature compensation feature are integrated.
 19. Anautostereoscopic display apparatus comprising: a spatial light modulatorcomprising: a plurality of pixels, each comprising: at least oneaperture having a first alignment feature compensation feature; and atleast one alignment feature aligning with the first alignment featurecompensation features with respect to a notional line; and a parallaxelement comprising an array of optical elements arranged over thespatial light modulator.